Patrick Lansdon and Michael Molumby will Present their Research on Thursday, 11/12/15
THE ROLE OF ENDOGENOUS MICROBIOTA IN SEIZURE-LIKE BEHAVIOR OF SHUDDERER, A DROSOPHILA VOLTAGE-GATED SODIUM CHANNEL MUTANT
It is widely recognized that mutations in genes encoding voltage-gated sodium (Nav) channels contribute to the etiology underlying various seizure disorders. Shudderer (Shu), a gain-of-function mutant for the Drosophila Nav channel gene, exhibits neuronal hyperexcitability and seizure-like behavioral defects, including spontaneous leg jerking, twitching, and heat-induced convulsion. Intriguingly, we have recently discovered that food supplemented with milk whey acts as a nutritional therapy, drastically suppressing these behavioral phenotypes. Microarray analysis revealed high levels of insulin receptor (InR) expression in Shu mutants relative to wild-type (WT) flies, indicating Shu has reduced insulin signaling. Following milk whey treatment, InR expression in Shu mutants returned to wild-type levels, suggesting milk whey increases insulin signaling. Because the endogenous gut microbiota are known to impact metabolic and developmental homeostasis through insulin signaling, we hypothesized that the microbiome plays a role in Shu phenotypes and their diet-dependent modification. Raising Shu mutants and WT flies in either antibiotic-containing or sterile food was sufficient to eliminate the gut microbiota. Further, both treatments were found to significantly suppress Shu behavioral phenotypes while having no obvious effect on WT behavior. Culturing extracts of homogenized flies on LB agar plates revealed drastic differences in the number and possibly the species of bacteria found in Shu and WT flies raised on conventional or milk whey-supplemented food. To confirm these results, we plan to perform high-throughput sequencing of the bacterial 16S ribosomal gene to identify differences in the gut microbiome composition of Shu and WT flies in the context of both conventional and milk whey-containing diets. This and future experiments are expected to provide us with a better understanding of the interplay between dietary therapy and the microbiome in the context of seizure disorders.
Homophilic protocadherin cell-cell interactions drive dendrite complexity
Growth of a properly complex dendrite arbor is a key step in neuronal differentiation and a prerequisite for neural circuit formation. Diverse cell surface molecules, such as the clustered protocadherins (Pcdhs), have long been proposed to regulate circuit formation through specific cell-cell interactions. Here, using transgenic and conditional knockout mice to manipulate g-Pcdh repertoire in the cerebral cortex, we show that the complexity of a neuron’s dendritic arbor is determined by homophilic interactions with other cells. Neurons expressing only one of the 22 g-Pcdhs can exhibit either exuberant, or minimal, dendrite complexity depending only on whether surrounding cells express the same isoform. Furthermore, loss of astrocytic g-Pcdhs, or disruption of astrocyte-neuron homophilic matching, reduces dendrite complexity cell non-autonomously. Our data indicate that g-Pcdhs act locally to promote dendrite arborization via homophilic matching and confirm that connectivity in vivo depends on molecular interactions between neurons, and between neurons and astrocytes.